For many reasons, fishermen are increasingly reluctant to retain and clean their catches for consumption as food, or even for mounting as trophies. In the latter case, photographs and the testimony of witnesses present at the time of the catch have frequently been considered adequate to attest to the fisherman's success, at least until a serious challenge has been raised against which no adequate proofs have sometimes been forthcoming. Rather than retaining the fish, the fishermen have increasingly returned them to the waters in which they were caught. This has been particularly true with respect to the fish caught in fishing tournaments.
Icthyologists and aquatic biologists research the eating habits, the mating habits and other life functions of various species of fish, in part by tagging fish which have been caught. A recognizable or identifiable tag is secured to the fish so that if the fish is subsequently caught or retrieved for study, various important data can be derived from the fact of the first catching of the fish, the location at which that occurred and the time span which has elapsed between the first and second catching. In many cases, fishermen have cooperated in this effort by tagging fish which they have caught and released.
Where a fish which may be a trophy or record fish is caught, the fisherman often has no immediate means of provably recording the fact of the catch, and of recording important data concerning weight, length or perhaps other characteristics of interest. Seldom does a sport fisherman carry with him in the boat, a sensitive and accurate scales by which a trophy fish which has been caught can be weighed, and no means is usually available in the boat for making a linear measurement of the fish. These circumstances tend to discourage a fisherman who has caught a fish which is potentially a trophy from releasing the fish soon enough after it is caught to be assured that the fish will remain alive.